The uplink of F-band Time-Division Long-Term Evolution (TD-LTE) base stations may be subject to the downlink barrage jamming, intermodulation interference, and spurious emission interference of a nearby heterogenous system base station (e.g. Global System for Mobile communication (GSM) 900, Distributed Control System (DCS) 1800, Personal Handy-phone System (PHS)base station). Therefore, signals received via TD-LTE system uplink may experience strong disturbance, which will greatly impact uplink performance of TD-LTE base stations.
In existing technologies, engineering methods (e.g. antenna insulation, antenna replacement, roof adjustment, or addition of anti jamming filter) are used to address disturbance caused by heterogenous systems in certain station sites. However, in many station sites, due to workload, difficulty, and impact on existing GSM network, the operators are not in favor of such engineering disturbance suppression methods. Besides, some heterogenous system disturbances originate from base stations of other operators. As different operators adopt mutually independent network configurations, it is impossible to address disturbances from base stations of other operators through engineering methods.
Current technologies can improve uplink performance of a TD-LTE system by means of frequency selection scheduling. Frequency selection scheduling in a LTE system can effectively solve degraded wireless transmission due to frequency selective decay in wireless channel environment. Frequency selection scheduling is based on the following principle: In each scheduling cycle, each user equipment (UE) is assigned the physical resource block (PRB) with the best sub-band channel quality, thus improving cell throughput and user awareness. Specifically, the base station (eNodeB) performs SRS channel estimation based on the detection reference sounding reference signals (SRS) sent by UE, and measures channel quality of each sub-band with such channel estimation. Next, it will start uplink frequency selection scheduling based on the channel quality of each sub-band.
However, SRS can be sent periodically or non-periodically by UE. The minimum transmission cycle defined in the 3rd Generation Partnership Project (3GPP) protocol is 5 ms, and this interval is even longer for non-periodic transmission. The narrow-band interferences from a heterogenous system are random and intensive in nature with the form of pulses, which means the interfering signals last for a very short period of time and typically occur within certain fixed frequency ranges. Such interfering signals are not smooth and will not cover the whole SRS transmission cycle. Therefore, the signal to interference plus noise ratio (SINR) obtained through SRS channel estimation is not able to reflect impact of narrow-band interference. Consequently, uplink frequency selection scheduling based on SRS channel estimation will not suppress narrow-band interference from a heterogenous system. It can therefore be concluded that existing technologies fail to solve interferences caused by a heterogenous system.